1. Field of the Invention
The present invention relates to a communication system wherein one master station transmits data to a plurality of slave stations in a time-division multiplex (TDM) system and each slave station transmits data to the master station in a time-division multiple access (TDMA) system. More particularly, it relates to a communication system wherein, if each slave station is to transmit a message signal of a different data quantity from the data quantity corresponding to a predetermined message area arranged in one radio burst signal in a radio frame, each slave station transmits that message signal without altering the composition of said radio burst signal or that of the radio frame.
2. Description of the Related Art
Instances of the prior art related to the present invention are disclosed in the Gazette of the Japanese Patent Laid-open No. 1990-203632 (Reference 1) and the Gazette of the Japanese Patent Laid-open No. 1989-272332 (Reference 2).
In the TDM system disclosed in said Reference 1, each slave station sets its frame composition such that the data in the slowest transmission speed is transmitted in one time slot of its frame, and this communication system, when communicating data of a fast transmission speed, divides the data, and allocates the divided data to message areas in a plurality of time slots to transmit the data.
The communication system disclosed in this Reference 1 cannot use the format of radio burst signals for the communication of data of 64 kbps, which is the commonly used transmission speed, because data of the slowest transmission speed, for instance data of 32 kbps or 16 kbps in transmission speed, are arranged in a prescribed message area within one radio burst signal.
The Reference 2 discloses a TDM system for communicating data of different transmission speeds, 64 kbps, 32 kbps and 16 kbps, and more particularly to a communication system flexibly adaptable to changes in data transmission speed. More specifically, this communication system concurrently uses one channel consisting of a prescribed number of bits for the communication of data of a fast transmission speed and that of data of a slow transmission speed. The slower the transmission speed of data, the greater the number of invalid bits among the total bits on that one channel, and this communication system multiplexes data by compressing those invalid bits.
The communication system disclosed in this Reference 2, because of the presence of those invalid bits, cannot increase the number of subscribers who can be served even if data of a slow transmission speed are communicated.